In the non-patent literature 1 below, there is description of a holographic recording system adapted to write information, having a hologram memory as a target. This system has a spatial light modulator (SLM) and a random phase mask (RPM) prepared separately, and incorporated in an optical system together with a reflection mirror, optical lens, and the like in between.
The spatial light modulator is adapted for modulations such as those of intensity, phase, and polarization of coherent light emitted from a laser light source. The spatial light modulator has a periodical structure, and modulated light from the spatial light modulator is diffracted. As light is diffracted, interferences occur between adjacent rays of light, resulting in a reduced efficiency in utilization of light. Further, there appear dc components of light carrying meaningless optical information. Such dc components of light have significant light intensities, developing exposure also in other regions than dc components, constituting a cause of malfunction when recording information I a medium or on a picture.
The random phase mask provides spatially random phase variations to flux of light modulated by the spatial light modulator, preventing occurrences of light diffraction or development of dc components.
Non-Patent Literature 1: 2005 Optical Society of America, OCTIS codes: (090.0090) Holography; (090.4220) Multiplex holography. Koji ISHIOKA et al., “Optical Collinear Holographic Recording System Using a Blue Laser and a Random Phase Mask”.